When electric cars become______, we’ll need to build more charging stations. [ ]

______ do you study for tests —I study_____listening to tapes.

Every one of us must know this: _________ we live can we save the earth．

The Smiths ______ their breakfastwhen the morning post came

What was your brother like when he was young— He _______ be quiet, but now he’s very outgoing.